For me the best option for editing Pweave files is Emacs using the noweb-mode. I use .Pnw for Pweave documents written with reST markup and .Plw for LaTeX markup. Here is what I have in my ~/.emacs.d/init.el to make Emacs recognize my Pweave documents correctly.

The code simply sets the documenation mode (noweb-doc-mode as rst-mode) as reStructuredText or LaTeX depending on the extension and the code mode as Python, so that the code chunks will be correctly formatted.